It is desired to develop a noninvasive or minimally invasive technique for preventing and diagnosing stenosis of a coronary artery causing heart disease which is one of three major diseases, cerebral aneurysm, or stenosis caused by a plaque of a carotid artery which may be a premonition thereof.
Stenosis of a coronary artery is a serious pathologic change that may lead to ischemic heart disease. A diagnosis of stenosis of a coronary artery is mainly Coronary Angiography (CAG) using a catheter. A diagnosis index of an organic pathologic change of a coronary artery includes Fractional Flow Reserve (FFR). The FFR is defined as a ratio of the maximum coronary blood flow where stenosis exists with respect to the maximum coronary blood flow where stenosis does not exist. The FFR is substantially the same as the ratio of a stenosis distal portion coronary internal pressure with respect to a stenosis proximal portion coronary internal pressure. The FFR is measured by a pressure sensor provided at a catheter distal end. More specifically, a catheter operation is required to measure the FFR.
When the analysis of stenosis of the coronary artery can be performed with a heart CT, this is minimally invasive, and can reduce the burden imposed on the patient and save the medical cost as compared with the measurement of the FFR with the catheter operation. However, in the heart CT, only the index based on the size of a plaque region or a thrombus region included in a CT image can be measured in a minimally invasive manner. If a pressure difference and the like before and after the thrombus can be measured based on the CT image by structural fluid analysis, the effect exerted by the thrombus (or plaque) is expected to be quantified.
Medical imaging techniques such as ultra-fast CT, cine angiography, MRI (magnetic resonance image method), ultrasonic imaging method, SPECT (single photon emission tomography), PET (positron emission tomography), and the like have been developed in terms of clinical aspect as a dynamic evaluation of coronary circulation, and are used for evaluation of diagnosis and treatment methods.
However, it is difficult for a medical image diagnosis apparatus to accurately recognize coronary microvessels. Even if a blood vessel shape is clear, a medical image may include noises, and the threshold value setting at the boundary of a living tissue may be ambiguous. As described above, a blood vessel shape obtained by the medical image diagnosis apparatus involves uncertainty.
When a medical image diagnosis apparatus is utilized in a clinical application, analysis is often performed on the target of only a thick region of coronary artery from the origin of the aorta at the upstream of the coronary microvessels. Since the bloodstream of the coronary artery is also greatly affected by the tonus of the coronary microvessels, it is the problem to appropriately set boundary conditions of fluid analysis such as the volume of flow or pressure at the exit of the coronary artery of the thick region or the rate of change thereof. The bloodstream of the coronary artery receives mechanical factors of pulsation of the heart (overall movement caused by pulsation, and forced displacement or external force due to local expansion and contraction, twisting, and shearing deformation). With the fluid analysis alone, the effect of the mechanical factors such as pulsation of the heart cannot be taken into consideration, and therefore, the volume of flow distribution of the bloodstream and the internal pressure distribution cannot be accurately measured. On the other hand, a structure-fluid interaction analysis is also carried out on the heart and the blood vessel system captured in an image in view of the effects of the mechanical factors. However, even when the structure-fluid interaction analysis is performed, it is often difficult to correctly set the material model of the blood vessel and the plaque and the boundary condition at the entrance and the exit of the blood vessel in the fluid analysis of the blood (including contrast agent). When there is a microvessel that is not captured in the image, the effect of the microvessel given to the bloodstream cannot be taken into consideration. For this reason, the analysis result of the structure-fluid interaction analysis may not be reproducing actual bloodstream and blood vessel deformation. In a case where the boundary condition, the load condition, and the material model are not appropriate, or in a case where the blood vessel involves great movement, there may be a problem in the convergence and the analysis stability. As described above, in conventional structural fluid analysis of blood vessels, it may be required to have large analysis resources and it may take an analysis time, or the error of the analysis result may increase, and therefore, there may be a problem in the utilization in actual clinical scenes.